1. Field of the Invention
This invention relates to a method of manufacturing a molding material, a method of manufacturing a molded body, a method of manufacturing a sintered body, a molding material, a molded body and a sintered body that can be utilized for ceramics or powder metallurgy.
2. Related Art Statement
Aqueous injection molding technique using agar has been known in the fields of ceramic powder molding and powder metallurgy. Particularly, in the injection molding method of ceramic powder, it has been known to mold a ceramic powder by using a binder constituted with water and agar. For example, in Japanese Patent No. 2604592 (U.S. Pat. No. 4,734,237), a basic patent in the relevant field, a metal powder or ceramic powder, an agaroid gel-forming material and water are mixed, and the mixture is heated to a temperature exceeding the gel point of the agaroid gel-forming material. The mixture is then molded at a temperature lower than the gel point thereby obtaining a molded body comprising the ceramic powder or metal powder. For example, an aqueous agar solution is admixed to a mixture of an alumina powder and deionized water, the mixture is mixed under heating at 77° C. and injection molded, and the resultant molded body is sintered at 1600° C. Further, Japanese Patent No. 3105225 (U.S. patent application Ser. No. 748,151: PCT/US92/06799) also discloses a similar manufacturing method.
The present inventors have made a study, based on the patents described above, for obtaining a molded body of a complicate shape and its sintered body by the injection molding method. In the course of the study, it was observed that scattering was caused in the strength of the sintered body or the strength of the sintered body was lowered depending on the conditions. When the sintered body showing a low strength was analyzed and studied, it was found that lowering in the relative density was extremely small. Further, in the relevant field of the art using agar and water as the binder, the amount of agar is extremely small compared with those of conventional resin binders or wax binders. In addition, in the course of elevating the temperature of the molded body, since agar is easily released together with water, it is considered that no special degreasing step is required. That is, in the technique of using agar and water as the binder, it would be unlikely that remarkable lowering of the strength in the sintered body is caused depending on mixing, molding and degreasing conditions, and the cause therefor was unknown. Since ceramics are brittle, it is desirable to increase the strength in view of avoiding the risk leading to fracture.